Photosensitive silver halide microcapsules



United States Patent 3,443,948 PHOTOSENSITIVE SILVER HALIDEMICROCAPSULES Thomas Toplica Bryan, White Bear Lake, Minn., assignor toMinnesota Mining and Manufacturing Company, St. Paul, Minn., acorporation of Delaware No Drawing. Filed July 12, 1965, Ser. No.471,421

Int. Cl. G03c 3/00; G03 1/52 U.S. Cl. 9667 5 Claims ABSTRACT OF THEDISCLOSURE This invention relates to light sensitive microcapsules, thecapsule wall comprising gelatin, silver halide and a water soluble colorcoupler or a bleachable dyestutf and having water immiscible materialsencapsulated within.

This invention relates to novel light sensitive microcapsules, theirpreparation and use. In one aspect this invention relates to filledmicrocapsules having a light sensitive shell.

The preparation of microcapsules having a shell of a gelled hydrophiliccolloidal material has been described in U.S. Patents Nos. 2,800,457 and2,800,458 and Belgian Patent No. 628,650. Oil-containing microcapsulesmay be produced by dispersing the oil in an aqueous solution of gellinghydrophilic colloidal material capable of coacervation. By addition of acoacervating agent a colloidal film can be produced around each oildroplet, and the colloidal film can then be gelled by cooling. In onetechnique, a gelatin derivative with pH-dependent solubility may be usedas the gelling hydrophilic colloidal material, coacervation beingachieved by acidification of the emulsion. Microcapsules having gelatinshells may be treated with dichromate solution to impartphotosensitivity, such microcapsules having a lesser ability to swell inwater after light exposure, as set forth in U.S. Patent No. 3,001,873.

It is an object of this invention to provide a novel light sensitivemicrocapsule.

Still another object of this invention is to provide a light sensitivemicrocapsule which can be processed by known photographic techniqueswithout rupturing the microcapsule wall.

A further object of this invention is to provide methods for preparingphotosensitive microcapsules.

Yet another object of this invention is to provide useful lightsensitive constructions incorporating photosensitive microcapsules.

Other objects and advantages will be apparent from the followingdescription and examples.

In accordance with this invention it has been found that light sensitivesilver halide may be incorporated into an aqueous system containing agellable hydrophilic material capable of serving as a carrier for silverhalide in a photographic construction and useful in the preparation ofmicrocapsules and that microcapsules may be prepared therefrom. Theresulting microcapsules are thereby rendered photosensitive by virtue ofthe silver halide contained in the gelable hydrophilic material formingthe water permeable microcapsule wall. It has also been found that anyof the various techniques for preparing microcapsules from gelablehydrophilic materials, such as gelatin, gelatin derivatives, etc., canbe used for purposes of this invention. In general, the preferredtechniques involve coagulation or coacervation of the gelablehydrophilic material from an aqueous continuous phase about the waterimmiscible droplets of the discontinuous phase and the recovery of themicroencapsulated water immiscible droplets. Preferred microcapsulesnormally have a diameter no greater than about 10 microns, usually from1 to 10 microns. It is often desirable that the aqueous phaseadditionally contain sensitizers, stabilizers, dyestuffs, colorcouplers, and other substances advantageously used in silver halideemulsions forphotographic purposes, thereby including such materialsinto the microcapsule wall. The amount of siliver halide incorporatedinto the microcapsule wall is controlled by the concentration of silverhalide in the aqueous system containing gelable hydrophilic material,the ratio of silver halide to gelable hydrophilic material beingdetermined by the desired use of the resulting microcapsules.

In Belgian Patent No. 628,650 microcapsules are prepared from anygelatin derivative which can be coagulated in an acid medium and whichcan be formed through reaction of gelatin with an aromatic or aliphaticcompound having a group which can react with gelatin. Such a gelatinderivative with pH dependent solubility is defined as a gelatinderivative which is soluble in aqueous alkaline media but which can bedeposited from such solutions by acidification to a pH below 5. Examplesof such acid-coagulatable gelatin derivatives include the products ofthe reaction of gelatin with aromatic and aliphatic acid anhydrides(e.g., phthalic acid anhydride, trimellitic acid anhydride, pyromelliticacid anhydride, maleic acid anhydride, succinic acid anhydride, etc.),with compounds containing reactive halogen atoms (e.g., benzenesulphochloride, p-chlorobenzene sulphochloride, mchlorosulphonyl benzoicacid, p-aminobenzene sulphofluoride, m-fluorosulphonyl benzoylacetamide,benzoyl chloride, p-brornocarbonyl benzoic acid, p-bromomethyl benzoicacid, methoxyethyl chloroformate, mucochloric acid, etc.), withisocyanates (e.g., phenyl isocyanate, pbromophenyl isocyanate, naphthylisocyanate, etc.) and with N-aryl vinyl sulphonamides (e.g., N-vinylsulphonic acid anilide, N-vinyl sulphonic acid-N-methyl anilide, etc.).

The photosensitive microcapsules of this invention are furthercharacterized by the presence of water insoluble or water immisciblecontents, either in solid or liquid form. When the contents is an oilsoluble coupler, the microcapsules may be exposed to light to generatesilver nuclei which can then serve to actuate or catalyze a developmentor a color coupling reaction either in the water permeable microcapsulewall or at the interface between the microcapsule wall and theencapsulated contents, i.e., selective color formation. Developers andother reactants, such as those required for a color coupling reaction,may be introduced by diffusion into the microcapsule wall, using thewell known techniques of silver halide photography. If the contents ofthe microcapsule are colored (e.g., colored glass beads, oil solubledyestuffs (Helo Oil Red R), carbon, titanium dioxide, etc.), selectivemasking of the encapsulated material can be obtained by photographicdevelopment to provide a dense silver deposit or color development inthe microcapsule walls. If a colored material capsule of selectivedecomposition or color conversion in a reaction conducted in thepresence of silver nuclei (e.g., bleachable dyestuffs used in the silverdye bleach process) is incorporated in water insoluble form as themicrocapsule contents or in water soluble form into the microcapsulewall, the light exposed microcapsules can be developed by treatment withsuitable materials which can diffuse into the microcapsule wall toinitiate the desired reaction. In all such reactions the water permeablegel microcapsule wall permits diffusion of water soluble reactants intothe wall, where a reaction may be made to occur with materials containedin the wall or with the water immiscible contents at the Wallcontentsinterface. Using the various mechanisms of color forming, coloralteration, color destruction and color masking, copysheets having themicrocapsules of this invention coated thereon, preferably inconjunction with a water permeable binder such as gelatin, orincorporated therein can be used to record visible images withoutrequin'ng rupture or migration of the mircocapsules.

EXAMPLE 1 In U.S. Patent No. 2,800,457 the coacervation of gelatin iscaused by dilution and/or by adjusting the pH of a mixture of twocolloids of differing charge. Using silver halide in this procedurephotosensitive microcapsules can be prepared, starting with thefollowing two colloids.

The silver halide emulsion was prepared according to the proceduresdescribed in Photographic Chemistry, P. Glafkides, vol. I, pages341-353. The two colloids A and B were mixed, the pH being adjusted to6.8 by adding 10 percent NaOH. The resulting mixture was then dilutedwith 30 cc. water. At a tempenature of 50 C. slow addition of 10 percentacetic acid was made until the pH reached 4.0, at which point the silverhalide emulsion coagulated around the finely dispersed oil droplets toform microcapsules. The microcapsules were washed several times withwater by decantation.

The above procedure was repeated, using a 10 percent color couplersolution in tricresylphosphate as the dispersed oil phase, the colorcoupler being l-(2',4',6'-trichlorophenyl) 3 [3"-(2,4'-di-tertiaryamylphenoxyacetamido)benzamido]-5-pyrazolone, shown as Compound 7 inU.S. Patent No. 2,600,788. The coating mixture was prepared bydispersing the microcapsules in water containing 10 weight percentpolyvinyl alcohol as hinder, the concentration of microcapsules in themixture controlling the density in the final sheet. These microcapsuleswere coated onto opaque paper and transparent film base with a reverseroll coater, the water permeable binder (e.g., polyvinyl alcohol,gelatin and the various materials described in U.S. 3,189,453) beingemployed to provide adhesion to the substrate. After air drying thecoated sheets were exposed to light through a continuous tone wedge anddeveloped by the same techniques employed with color couplers inconventional silver halide photography, thereby producing a colorrendition of the wedge pattern. The color coupling development techniqueusing primary aromatic amino silver halide developer is shown in U.S.Patent No. 2,600,788.

EXAMPLE 2 In U.S. Patent No. 2,800,458 gelatin microcapsules have beenprepared by a salt-coacervation technique. The process of flocculatingsilver halide by the use of ammonium sulfate is described in U.S.2,618,556. This method was modified to prepare photosensitivemicrocapsules by the following procedure.

37 weight percent aqueous solution of formaldehyde r 25 Water liters 3 Aand B were homogenized at 50 C. to provide an intimate dispersion of theoil droplets in the aqueous phase. The ammonium sulfate solution C wasthen added slowly with stirring and cooling. The silver halide emulsiondeposited around each oil droplet to form photosensitive microcapsuleshaving an oblong shape.

EXAMPLE 3 Anionic soap coagulation of silver halide emulsion for Washingwater soluble residues from the emulsion is described in U.S. PatentsNos. 2,489,341 and 2,527,260. The addition of small amounts of anioniccompounds to gelatin emulsions will cause separation of a proteinanionicsoap complex. This technique has now been employed to encapsulate oilparticles with silver halide emulsions.

Water cc 1,000 Silver halide emulsion (as in Example 1) grams 67Tricressylphosphate cc 20 Anionic surfactant (a secondary sodium alkylsulfate, Teepol 610) cc 15 Water cc 30 To mixture A, acidified to pH 2.3with 0.01 normal sulfuric acid, mixture B was added slowly withstirring. A heavy silver halide gelatin shell formed around thetricresylphosphate oil droplets, forming photosensitive microcapsules.

EXAMPLE 4 Gelatin derivatives can also be coagulated by changing pH, asis described in U.S. Patent Nos. 2,481,650; 2,614,- 928; 2,614,929;2,728,662; 2,787,545; 2,956,880; 3,132,- 945 and 3,138,461. The use ofsuch coagulation techniques for the production of microcapsules frommodified gelatin or gelatin derivatives is shown in Belgian Patent No.628,650.

60 cc. of tricressylphosphate was mixed with 67 grams of silver halideemulsion (as in Example 1 with the substitution of phthalated gelatin,Rousselot Gel 14382, for the unmodified gelatin), and 300 cc. of waterat 30 C. was added with cautions stirring. About 20 cc. of 1 percentsulfuric acid was then added slowly until the pH reached 3.5. Thecoagulated material was then cooled to room temperature, andphotosensitive microcapsules were separated by decantation.

EXAMPLE 5 60 cc. of oil (tricresylphosphate) was mixed with 300 cc. ofwater at 38 C. and grams of the silver halide emulsion of Example 1 toproduce an oil dispersion. To this dispersion was slowly added 66 cc. ofa 3 percent aqueous solution of dodecyldiphenyl ether ton $0.11

the ether being an anionic surfactant. Because the gelatin is positivelycharged, the anionic surfactant serves as a satisfactory coagulant. Theaddition of a few drops of 10 percent sulfuric acid caused the gelatinemulsion to coagulate about the minute oil droplets at a pH of 3.7 andprovide a coagulate of somewhat oblong shaped microcapsules. By raisingthe pH to 4.6 with 10 percent sodium hydroxide the microcapsules assumeda more spherical shape. When the pH was raised to 4.8 by furtheraddition of sodium hydroxide the gelatin coagulant redissolved, only toreform about the oil droplets as the pH was again lowered to 4.0 withthe introduction of more sulfuric acid.

EXAMPLE 6 60 cc. of tricresylphosphate was mixed with 100 cc. of silverhalide emulsion (as in Example 1) and 300 cc. of water at 38 C. to forman oil-in-water emulsion. To the emulsion was slowly added 38 cc. of 2.5weight percent aqueous solution of the water soluble copolymer of methylvinyl ether and maleic anhydride having a specific viscosity of l.0l.4in solution of 1 gram per 100 milliliters of methyl ethyl ketone at 25C. (Gantrez AN 139, General Aniline and Film Corporation), a gelatincoagulant, the pH being lowered to 4.3 by addition of diluted sulfuricacid. A gelatin-silver halide deposit formed around the oil droplets,producing photosensitive microcapsules. This example illustrates the useof a polymeric polyelcctrolyte as the gelatin coagulant inphotosensitive microcapsule preparation.

EXAMPLE 7 This example will illustrate the incorporation of a watersoluble color coupler into the photosensitive microcapsule shell wall.

Dibutyl phthalate cc 60 The silver halide emulsion of Example -1 cc 100Water cc 300 Color coupler solution containing 20 cc. methyl alcohol,150 cc. Water, 2 mols/mol coupler of 2 N NaOH cc 20 Magenta colorcoupler of the formula grams 110 i CH3(CH2)IFCHCNH(|CH2 SO H N 0:0

The color coupler solution was prepared from grams of this color couplercompound. Other suitable couplers are described in US. 2,425,503;2,768,894 and 2,829,575. Parts A and B were admixed, and 40 cc. of 2.5weight percent solution of the water soluble copolymer of methyl vinylether and maleic anhydride (specific viscosity of 1.0-1.4 in solution of1 gram per 100 milliliters of methyl ethyl ketone at 25 C.). The pH wasadjusted to 4.3 with dilute sulfuric acid, causing coagulation of thegelatin and formation of photosensitive microcapsules containing thecolor in the capsule shell. When coated onto suitable sheets thesemicrocapsules were exposed to a light image and developed to form acolor reproduction, as described in Example 1.

EXAMPLE 8 This example illustrates the encapsulation of hydroquinone, acommon photographic developer, in the photosensitive microcapsules ofthis invention.

Silver halide emulsion (as in Example 1) cc 67 Water cc 1000 10 percentby weight of hydroquinone in tricresylphosphate cc 60 Anionic surfactant(a secondary sodium alkyl sulfate, Tee-pol 6-10) cc 15 Water cc 30 Thesilver halide emulsion A was acidified with 0.01 N sulfuric acid to a pHof 2.3. Solutions A and B were mixed and homogenized, and solution C wasadded sloW- ly with stirring. A gelatino-silver halide coagulate formedabout the droplets of the tricresylphosphate-hydroquinone oil phase,producing photosensitive microcapsules which could be recovered andcoated onto sheets as described in Example 1. The sheets coated withmicrocapsules were exposed to a light image and developed with a 10weight percent sodium carbonate solution to form black silver images.

EXAMPLE 9 This example illustrates the incorporation of a coloredbleachable azo dye in the photosensitive microcapsule Following themixing and coagulating techniques of Example '1 photosensitivemicrocapsules were produced. To this dispersion of microcapsules wasadded 50 grams of gelatin in 250 cc. of water to form a coatingcomposition, which was then coated onto polystyrene film base. Afterexposing the sheet to light and developing by the conventional silverdye bleach process, the cyan microcapsules were selectively decolorizedin the light exposed areas.

EXAMPLE '10 This example illustrates the incorporation of a coloredbleachable azo dye in the photosensitive microcapsule wall and an oilsoluble color coupler as the microcapsule contents.

Gum arabic gramsn 10 Water cc 10 weight percent tricresylphosphatesolution of the color coupler of Example 1 -cc 40 Silver halide emulsion(as in Example 1) grams 67 2 Weight percent aqueous solution the cyanbleachable azo dyestuif of Example 9 cc 30 Following the same techniqueas in Example 9 photosensitive microcapsules were produced and thencoated in a gelatin binder onto a sheet. After exposure to a light imagethe sheet was developed by conventional photographic techniques to format the inner wall interface a col-or from the color coupler contents inthe light struck microcapsules and then by silver dye bleach techniqueto bleach the cyan azo dye in the light exposed microcapsule walls.

EXAMPLE 11 This example illustrates the encapsulation of solids in thephotosensitive microcapsules of this invention.

Colored glass geads having a particle size of 10 to 30 microns(1.85-1.95 index of refracti-on) grarns 10 Silver halide emulsion (as inExample '1) cc 100 Water cc 300 After parts A and B were prepared andadmixed 3 8 cc. of a 2 weight percent solution of the Water solublecopolymer of methyl vinyl ether and maleic anhydride of Example 6, thepH being lowered with dilute sulfuric acid to 4.3 to etfect coagulationof the gelatin about the dispersed colored glass beads. When theresulting photosensitive microcapsules were coated in a gelatin binderonto a sheet, as in Example 9, exposed to a light image and developedwith conventional silver developer, the black silver masked the color ofthe beads in the image areas, forming a visible reproduction of thelight image.

Various other embodiments of the present invention will be apparent tothose skilled in the art without departing from the scope thereof.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows.

I claim:

1. A photosensitive microcapsule having a wall comprising gelatin,photosensitive silver halide, and an organic compound capable ofeifecting a color change in a reaction conducted in the presence ofsilver nuclei and having water immiscible contents encapsulated therein.

2. A photosensitive microcapsule having a wall comprising gelatin,photosensitive silver halide and a water soluble color coupler andhaving water immiscible contents encapsulated therein.

3. A photosensitive microcapsule having a wall comprising gelatin,photosensitive silver halide, and a colored bleachable azo dye andhaving Water immiscible contents encapsulated therein.

4. The photosensitive capsule of claim 3 in which said water immisciblecontents comprises a color coupler.

5. The photosensitive microcapsule of claim 3 in which said coloredhleachable azo dye is a water soluble bleachable dyestuit of the typeuseful in the silver dye bleach process.

References Qited UNITED STATES PATENTS 2,800,457 7/1957 Green et a1.117-164 2,953,454 9/1960 Berman 11734 3,001,873 9/1961 Foris 96753,276,869 10/1966 McCune 9697 3,306,747 2/1967 Haas 96-29 3,369,900 2/1968 Taylor 96-76 NORMAN S. TORCHIN, Primary Examiner.

M. F. KELLEY, Assistant Examiner.

US. Cl. X.R. 9697 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIONDate: May 13 1969 Patent No. 3 4 43 9 Thomas Toplica Bryan It iscertified that error appears in the aboveidentified patent and that saidLetters Patent are hereby corrected as shown below:

Column 6, line 23, for "10" read 8O and line 7 4, for "geads" read beadsSIGNED AND SEALED FEB 2 41970 J Most:

MEFlewhcrJr. WILLIAM E- W, JR.

Dominion of Patents Attosfing Officer

